The majority of present day integrated circuits (ICs) are implemented by using a plurality of interconnected field effect transistors (FETs), also called metal oxide semiconductor field effect transistors (MOSFETs), or simply MOS transistors. A FET includes a gate electrode as a control electrode and spaced apart source and drain electrodes between which a current can flow. A control voltage applied to the gate electrode controls the flow of current through a channel between the source and drain electrodes.
The gain of an FET, usually defined by the transconductance (gm), is proportional to the mobility of the majority carrier in the transistor channel. The current carrying capability of an MOS transistor is proportional to the transconductance times the width of the channel divided by the length of the channel (gmW/l). FETs are usually fabricated on silicon substrates with a (100) crystallographic surface orientation, which is conventional for silicon technology. For this and many other orientations, the mobility of holes, the majority carrier in a P-channel FET (PFET), can be increased by applying a compressive longitudinal stress to the channel. A compressive longitudinal stress can be applied to the channel of FET by embedding an expanding material such as pseudomorphic SiGe in the silicon substrate at the ends of the transistor channel [For example, see IEEE Electron Device Letters v. 25, No 4, p. 191, 2004]. A silicon germanium (SiGe) crystal has a greater lattice constant than the lattice constant of a silicon crystal, and consequently the presence of embedded SiGe causes a deformation of the silicon matrix that, in turn, compresses the silicon in the channel region. Although a number of techniques are know for embedding SiGe to enhance the mobility of majority carrier holes in PFETs, none has yet achieved the increase in mobility potentially attainable with embedded silicon germanium.
Accordingly, it is desirable to provide a field effect transistor having enhanced majority carrier channel mobility. In addition, it is desirable to provide a method for fabricating a P-channel field effect transistor having enhanced hole mobility. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.